A binary star, which was always believed to have existed, has finally been discovered by researchers at the Center for Astrophysics, Harvard and Smithsonian. The findings published in the Royal Astronomical Society’s Monthly Notices shows how unusual type of stars emerge and evolve in cosmos. Kareem El Badry, a postdoctoral fellow at the Center for Astrophysics, discovered the new stars by using the Shane Telescope at Lick Observatory in California and data from several astronomical surveys, reported phys.org. Describing the discovery as exciting, El- Badry said it’s a missing stellar evolutionary link in the binary of star formation. Usually, when stars die, they turn into a white dwarf- a small dense object that has contracted and dimmed after burning through all its fuels. In rare instances, stars can also turn into extremely low mass (ELM) white dwarfs. Now, as per stellar evolution calculation, these ELM white dwarfs which are one-third of the sun’s mass would seem to be more than 13.8 billion years old- older than the age of the universe itself which is physically not possible.
The universe is not just old enough to make these stars by normal evolution.
So far, astronomical studies have shown that the only way to form ELM white dwarf is by a binary companion. While some studies show the gravitational pull from a nearby star companion star could eat away a star more quickly, there’s no full-proof evidence to it as yet.
Astronomers have also observed regular, massive stars like the Sun turn into a white dwarf through the process of cataclysmic variables. In some cases, ELM white dwarf was seen as a companion to white dwarf but there has been nothing to show the transitional phase of evolution when the star has most of its mass and has nearly turned into an ELM white dwarf
To find this missing link, EL Badry in 2020 started his search for a star that had long alluded scientists: the pre-ELM white dwarf.
He used the data from Gaia, the space-based observatory launched by the European Space Agency, and the Zwicky Transient Facility at Caltech, to narrow down his search from a billion stars to 50 probable candidates
El Badry then followed it with close observation of 21 of the star. He started gaining success in his mission as 100 per cent of the candidates were the pre-ELMs that he was looking for. The stars were puffed and bloated and in the shape of an egg because the gravitational pull of the other star distorts their spherical shape.
During the research, 13 of the stars showed signs that they were losing mass to their companion while 8 did not lose the mass. However, each one of them was hotter than previously observed cataclysmic variables.
After the recent success, EL-Badry now plans to continue studying the pre- ELM white dwarf and may even follow up on the other 29 stars he had previously discovered.
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